Background Bone Mineral Density is frequently measured during the assessment and management of adolescents with Eating Disorders (EDs) such as Anorexia Nervosa (AN) and Atypical AN(AAN), which negatively affects the physical and mental developments of children at a vital phase of growth. Compromised bone accrual in adolescents has significant long-term implications on their peak bone mass and overall bone health in their later years. To date there has been no study on the effect of AN and AAN on BMD in young Asian adolescents.

Objectives In this retrospective study, we compare BMD and baseline characteristics in Adolescents from Singapore with AN and AAN, to find any difference in BMD Z-score between AN and AAN, and any predictive factors for low bone density in adolescents with EDs.

Methods We reviewed electronic medical records for all patients below the age of 18, who were treated for Eating Disorders at KK Women’s and Children’s Hospital between 2010 and 2020 (n=507).

Results 318 AN and 141 AAN cases were identified within the study period. Mean age of all cases is 14.08 ± 1.49 years with mean duration of illness being 8.06 ± 6.15 months. Females made up 92.8% of AN cases, compared to 84.4% of AAN cases (χ²(1)=7.739 ; p= 0.005).%mBMI at presentation was significantly lower for AN than AAN (74.55 ± 7.27 versus 97.12 ± 9.95, t(210)= - 24.18, p < 0.001). 29% of AAN patients were premorbidly overweight (max IBW > 120%), compared to 4.6% of AN patients (χ²(1)= 42.97 ; p < 0.001). There were significantly higher BMD Z-scores in AAN compared to AN for both the spine (1.55± 1.63 versus 0.29± 1.67, t(179)= -4.22, p < 0.001) and femur (0.48± 0.93 versus 0.23± 1.19, t(194)= -3.63, p < 0.001) region. In our linear regression model, BMD Z-score was not associated with duration or magnitude of weight loss as well as duration of amenorrhea or overweight status.

Conclusions From the findings of our study, we conclude that asian adolescents with AAN demonstrated higher BMD Z-scores for both spine and femur compared to their AN counterparts. There was no predictive factors for low bone density. These findings may be instructive in informing guidelines for the management of Asian adolescents with AN and AAN.